The present invention relates to a method for alarming decrease in tire air-pressure and an apparatus used therefor. More particularly, it relates to a method for alarming decrease in tire air-pressure and an apparatus used therefor with which it is possible to accurately perform cornering correction and to improve the accuracy of detecting a decompressed condition of a tire.
A conventional apparatus for detecting decrease in tire air-pressure (DWS system) determines a decompressed condition of a tire based on information of four ABS wheel speed sensors. In case a vehicle performs cornering, the load will be shifted to the outside owing to the effect of lateral acceleration. Since the respective longitudinal load and slip ratio of the right and left tires are different at that time, it is impossible to determine a decompressed condition. In order to cope with problem, a conventional DWS performs cornering correction by obtaining a cornering radius (turning radius) based on a wheel speed ratio of the inner and outer following wheels (which are the rear wheels in the case of a FF vehicle and the front wheels in the case of a FR vehicle) and calculating an amount of change in longitudinal load and an amount of change in slip ratio accompanying the shift of load on the basis of the obtained value.
However, while a difference in rotation of the right and left following wheels will be caused as a result of a decompressed condition of either following wheel, it cannot be immediately determined whether this difference in rotation is due to a decompressed tire or merely due to cornering. Since it is rarely the case that cornering movements will last for longer than several tens of seconds when driving on a public road, wheel ratios of right and left following and driving wheels are obtained for approximately one minute and a decompressed condition of the following tire is determined in case a difference between these values exceeds a specified value.
It will therefore take approximately one minute for determining whether the difference in rotation is due to cornering or the difference in rotation is due to a decompressed tire when determining a decompressed condition of the tire. Though very rare, it might happen that malfunctions in performing determination occur in the case of certain values for the longitudinal load or slip ratio, and erroneous alarm might be issued upon determining that the difference in rotation is due to cornering though actually due to a decompressed tire or vice versa, determining a decompressed condition of the tire though the vehicle is actually performing cornering.
The present invention has been made in view of these facts, and it is an object of the present invention to provide a method for alarming decrease in tire air-pressure and an apparatus used therefor which is capable of accurately performing cornering correction and to improve the accuracy of detecting a decompressed condition.
In accordance with a first aspect of the present invention, there is provided an apparatus for alarming decrease in tire air-pressure based on rotational information obtained from tires attached to a four-wheeled vehicle, comprising: a rotational information detecting means for detecting rotational information of each tire; a steering angle detecting means for detecting a steering angle; a memory means for storing the rotational information of each tire and the steering angle; a turning radius calculating and processing means for calculating a turning radius based on the rotational information of each tire; a judged value calculating and processing means for calculating a judged value based on the rotational information of each tire; and a correction means for correcting the turning radius in case it has been determined by the steering angle detecting means that the vehicle is in a straight-ahead driving condition though the driving condition of the vehicle is a turning condition when being based on the turning radius obtained on the basis of the rotational information.
In accordance with a second aspect of the present invention, there is provided an apparatus for alarming decrease in tire air-pressure based on rotational information obtained from tires attached to a four-wheeled vehicle, comprising: a rotational information detecting means for detecting rotational information of each tire; a steering angle detecting means for detecting a steering angle; a memory means for storing the rotational information of each tire and the steering angle; a turning radius calculating and processing means for calculating a turning radius based on the rotational information of each tire; a correction means for correcting the turning radius in case it has been determined by the steering angle detecting means that the vehicle is in a straight-ahead driving condition though the driving condition of the vehicle is a turning condition when being based on the turning radius obtained on the basis of the rotational information; and a decompression determining means for determining a decompressed condition of a tire in case a correction coefficient for the turning radius as obtained by the correction means is not less than a threshold.
In accordance with a third aspect of the present invention, there is provided a method for alarming decrease in tire air-pressure based on rotational information obtained from tires attached to a four-wheeled vehicle, comprising the steps of; detecting rotational information of each tire; detecting a steering angle; storing the rotational information of each tire and the steering angle; calculating a reciprocal of a turning radius based on the rotational information of each tire; calculating a judged value based on the rotational information of each tire; and correcting, when performing correction of the judged value for decompressed condition due to cornering, the turning radius in case it has been determined on the basis of the steering angle that the vehicle is in a straight-ahead driving condition though the driving condition of the vehicle is a turning condition when being based on the turning radius obtained on the basis of the rotational information.
In accordance with a fourth aspect of the present invention, there is provided a method for alarming decrease in tire air-pressure based on rotational information obtained from tires attached to a four-wheeled vehicle, comprising the steps of: detecting rotational information of each tire; detecting a steering angle; storing the rotational information of each tire and the steering angle; calculating a turning radius based on the rotational information of each tire; correcting the turning radius in case it has been determined on the basis of the steering angle that the vehicle is in a straight-ahead driving condition though the driving condition of the vehicle is a turning condition when being based on the turning radius obtained on the basis of the rotational information; and determining a decompressed condition of a tire in case a correction coefficient for the turning radius as obtained during the correction process is not less than a threshold.
In accordance with a fifth aspect of the present invention, there is provided an apparatus for alarming decrease in tire air-pressure based on rotational information obtained from tires attached to a four-wheeled vehicle, comprising: a rotational information detecting means for detecting rotational information of each tire; a memory means for storing the rotational information of each tire; a calculating and processing means for calculating a judged value based on the rotational information of each tire; and a judged value correcting means for correcting the judged value based on a lateral acceleration obtained through a lateral acceleration sensor provided in the vehicle.
In accordance with a sixth aspect of the present invention, there is provided an apparatus for alarming decrease in tire air-pressure based on rotational information obtained from tires attached to a four-wheeled vehicle, comprising: a rotational information detecting means for detecting rotational information of each tire; a memory means for storing the rotational information of each tire; a calculating and processing means for calculating a judged value based on the rotational information of each tire; and a judged value correcting means for correcting the judged value based on a lateral acceleration obtained on a basis of values of a yaw rate sensor provided in the vehicle.
In accordance with a seventh aspect of the present invention, there is provided a method for alarming decrease in tire air-pressure based on rotational information obtained from tires attached to a four-wheeled vehicle, comprising the steps of: detecting rotational information of each tire; storing the rotational information of each tire; calculating a judged value based on the rotational information of each tire; and correcting the judged value based on a lateral acceleration obtained through a lateral acceleration sensor provided in the vehicle.
In accordance with a eighth aspect of the present invention, there is provided a method for alarming decrease in tire air-pressure based on rotational information obtained from tires attached to a four-wheeled vehicle, comprising the steps of: detecting rotational information of each tire; storing the rotational information of each tire; calculating a judged value based on the rotational information of each tire; and correcting the judged value based on a lateral acceleration obtained on a basis of values of a yaw rate sensor provided in the vehicle.